Substrate holding apparatus and substrate polishing apparatus

ABSTRACT

A substrate holding apparatus has a substrate holder body with a substrate holding side facing a polishing surface and holding a substrate on the substrate holding side and a retainer ring fixedly secured to the substrate holder body. The retainer ring is arranged to surround an outer periphery of the substrate held by the substrate holder body so that the retainer ring engages with the polishing surface radially outside the substrate as the polishing of the substrate is effected. The substrate holder body is provided with a membrane having inside and outside surfaces. The inside surface cooperates with a surface of the substrate holder body to define a fluid pressure chamber to which a fluid pressure is applied. The outer surface engages with the substrate held by the substrate holder body.

This is a Divisional Application of U.S. patent application Ser. No.10/972,579, filed Oct. 26, 2004, which is a Divisional Application ofU.S. patent application Ser. No. 09/917,732, filed Jul. 31, 2001 nowU.S. Pat. No. 6,890,402.

BACKGROUND OF THE INVENTION

The present invention relates to a substrate holding apparatus in whicha substrate is held when polished for flattening a surface thereof. Thepresent invention also relates to a polishing apparatus comprising theabove-mentioned substrate holding apparatus.

A semiconductor device fabricating process comprises forming a thin filmlayer on a wafer and forming minute patterns and holes in the layer.This process is repeated until a desired number of circuit layers areformed on the wafer. Therefore, raised and recessed portions are createdon or added to the surface of the wafer after formation of each circuitlayer. In recent years, semiconductor devices have become increasinglyminute and element structures of semiconductor devices have becomecomplicated. Further, there is a tendency to increase the number ofcircuit layers for logic type devices. As a result, raised and recessedportions on the surface of a semiconductor device increase in number anda difference in height between these portions also increases. This leadsto a problem such that during formation of a film on the wafer, anextremely thin film is formed over an undulating area containing theraised and recessed portions on the wafer and breaks in a circuit and anelectrical insulation defect between circuit layers are likely to occur,leading to a lowering of product quality and a lowering of yield.Although semiconductor devices can operate normally during an initialperiod of operation, they are not reliable when used over a long periodof time.

Raised and recessed portions on the wafer are also problematic in alithography process. That is, when an exposure surface of the wafercontains raised and recessed portions, the lenses of an exposure systempartially become out of focus, so that formation of minute patternsbecomes difficult.

For these reasons, the techniques for surface flattening in fabricatingsemiconductor devices have been increasingly becoming important. Ofvarious surface flattening techniques, the most important technique isCMP (chemical mechanical polishing), which comprises polishing by usinga polishing apparatus, in which while an abrasive liquid containingabrasive particles of silica (SiO2) or the like is supplied onto apolishing surface of a polishing pad, a semiconductor wafer is slidablyengaged with the polishing surface.

Conventionally, the polishing apparatus of the above-mentioned typecomprises a polishing table including a polishing pad having a polishingsurface and a wafer holder for holding a semiconductor wafer. The waferholder is adapted to hold a semiconductor wafer and press the waferagainst the polishing table under a predetermined pressure. The waferholder and the polishing table are moved relative to each other so thatthe semiconductor wafer is slidably engaged with the polishing surface,to thereby polish the wafer to a flat and mirror-finished surface.

In the above-mentioned polishing apparatus, when a relative pressuregenerated between the semiconductor wafer and the polishing surface ofthe polishing pad is not uniform over an entire surface of the wafer,insufficient or excessive polishing is likely to occur, depending on thepressure acting on each part of the wafer. Therefore, in order to applya uniform pressure to an entire surface of the wafer, an elasticmembrane made of rubber is provided on the wafer holder on a surfacethereof for holding a wafer, and a fluid pressure such as air pressureis applied to a back surface of the elastic membrane. In this case, acircumferential edge of the wafer surface corresponds to a boundarybetween a contact portion and a non-contact portion of the waferrelative to the polishing surface. Since the polishing pad is elastic,the pressure applied to a portion around the circumferential edge of thewafer surface becomes non-uniform, so that only the circumferential edgeof the wafer is polished in an excessive amount, and the wafer is causedto have a “dull” edge.

As a countermeasure, it has been proposed to use a wafer holder in whicha guide ring or retainer ring for holding an outer circumferential edgeof the wafer presses the polishing surface at a position outside thewafer. In this wafer holder, the retainer ring is pressed against thepolishing surface under fluid pressure such as air pressure.

FIG. 14 is a schematic illustration of a wafer holder of theabove-mentioned type, in which a fluid pressure is applied to a wafer soas to press the wafer against a polishing surface, and the fluidpressure is also applied to a retainer ring so as to press the retainerring against the polishing surface.

As shown in FIG. 14, a wafer holder 50 comprises: a wafer holder body 51defining an inner space; a wafer pressurizing mechanism 52 contained inthe inner space of the wafer holder body 51 and adapted to press asemiconductor wafer W against a polishing surface 61 of a polishingtable 60; a retainer ring 53 provided so that it is vertically movablerelative to the wafer holder body 51 and adapted to hold an outercircumferential edge of the wafer W; and a retainer ring pressurizingmechanism 54 for pressing the retainer ring 53 against the polishingsurface 61.

The wafer pressurizing mechanism 52, although not shown in detail,comprises an elastic membrane member which is made of an elasticmaterial such as rubber and is connected to the wafer holder body 51. Apressurized fluid such as pressurized air is supplied to the inside ofthe elastic membrane member so that the wafer W is pressed against thepolishing surface 61 under fluid pressure. The retainer ringpressurizing mechanism 54, although not shown in detail, also comprisesan elastic membrane member which is made of an elastic material such asrubber and is connected to the wafer holder body 51. A pressurized fluidsuch as pressurized air is supplied to the inside of the elasticmembrane member so that the retainer ring 53 is pressed against thepolishing surface 61 under fluid pressure. The wafer holder body 51 isconnected to a drive shaft 55 and the drive shaft 55 is adapted to bevertically moved by a lifting mechanism such as an air cylinder.

The lifting mechanism such as an air cylinder connected to the driveshaft 55 is operated so as to move the wafer holder body 51 as a wholeto a position close to the polishing table 60. While the wafer W is heldin proximity to the polishing surface 61, the pressurized fluid issupplied under a predetermined pressure to the wafer pressurizingmechanism 52, to thereby press the wafer W against the polishing surface61 of the polishing table 60. The pressure applied to the wafer W duringpolishing is adjusted to a desired value by adjusting the pressure ofthe pressurized fluid supplied to the wafer pressurizing mechanism 52.On the other hand, the pressurized fluid is supplied under apredetermined pressure to the retainer ring pressurizing mechanism 54,to thereby press the retainer ring 53 against the polishing surface 61of the polishing table 60.

Since the wafer W is pressed against the polishing surface 61 by using afluid pressure, it is possible to obtain a uniform pressure distributionacross an entire surface of the wafer W from the center to thecircumferential edge thereof. This enables uniform polishing of theentire surface of the wafer W. Further, during polishing, a pressuresubstantially equal to that applied to the wafer W is applied to theretainer ring 53 through the retainer ring pressurizing mechanism 54, sothat the polishing surface of the polishing pad outside the wafer W ispressed under a pressure substantially equal to that of the wafer W.Therefore, a uniform pressure distribution can be obtained continuouslyacross an area from the center of the wafer W to an outercircumferential portion of the retainer ring 53 outside the wafer W.Therefore, excessive or insufficient polishing at the circumferentialedge of the wafer W can be prevented.

In the above-mentioned conventional wafer holder in which both the waferand the retainer ring are pressed under fluid pressure, the retainerring is capable of moving in either a vertical (or perpendicular)direction or a lateral (or radial) direction relative to the waferholder body. That is, the retainer ring is capable of movingindependently of the wafer holder body. Movement of the retainer ringaffects uniformity in the polishing of an outer circumferential portionof the wafer surface. Although vertical movement of the retainer ring isnecessary for polishing, lateral movement of the retainer ring isunnecessary. Rather, lateral movement of the retainer ring isundesirable because it varies the distance between the retainer ring andthe circumferential edge of the wafer surface and impairs uniformity andstability in the polishing of the outer circumferential portion of thewafer surface.

Further, in the conventional wafer holder, since the surface of thewafer holder for holding a wafer is covered with the elastic membrane,it is required to form, for example, a suction cup-like configuration inthe elastic membrane so as to hold a wafer during transfer thereof. Whena wafer is held by the elastic membrane having a suction cup-likeconfiguration, warpage or deformation of the wafer occurs. Due towarpage of the wafer, the wafer can be broken during transfer thereof ora device structure formed on the wafer can be damaged. Further, sincethe wafer is held by indirect contact with the wafer holder through theelastic membrane, defects in holding of the wafer are likely to occurduring transfer of the wafer, leading to a lowering of operating rate ofthe wafer holder and a lowering of yield of wafers.

Further, in chemical mechanical polishing (CMP) utilizing an elasticpolishing pad and an abrasive liquid (slurry), the following problemarises. That is, when a wafer surface having raised and recessedportions is polished, the raised portions are polished in preference tothe recessed portions during an initial period of polishing, but afterthe raised portions are polished by a certain amount, the recessedportions are also gradually subjected to polishing (as well as theraised portions). Therefore, the difference in height between the raisedportions and the recessed portions cannot be easily reduced. That is,because polishing is conducted by using a relatively soft, elasticpolishing pad and a slurry type abrasive liquid containing a largeamount of free abrasive particles, chemical mechanical polishing iseffected on not only the raised portions, but also the recessed portionsof the wafer surface. Further, the effect of polishing varies, dependingon the density of raised and recessed portions.

Therefore, an attempt has been made with respect to polishing by using apolishing surface comprising fixed abrasive particles such as ceriumoxide (CeO2), which are bound by using a binder such as a phenol resin.In this polishing, the polishing surface is hard as compared to thepolishing pad conventionally used in chemical mechanical polishing, sothat the raised portions are polished in preference to the recessedportions and the recessed portions are unlikely to be polished.Therefore, absolute flatness of the wafer can be easily obtained.

However, a wafer holder suitable for a hard polishing surface comprisingfixed abrasive particles has not been developed. Generally, aconventional wafer holder for the hard polishing surface comprises arigid wafer holder body and an elastic backing pad provided on the rigidwafer holder body adapted to be engaged with a wafer to be held by thewafer holder. Although the elastic backing pad can absorb shocks on thewafer, it is difficult for the elastic backing pad to take care ofundulations on the hard polishing surface, whereby the undulations aretransferred to and affects the wafer surface to be polished.

SUMMARY OF THE INVENTION

In view of the above, the present invention has been made.

In accordance with the present invention, there is provided a substrateholding apparatus for holding a substrate and bringing it into contactwith a polishing surface so that the substrate is subjected to polishingby causing relative movement between the substrate and the polishingsurface, the apparatus comprising a substrate holder body having asubstrate holding side facing the polishing surface and holding asubstrate on the substrate holding side and a retainer ring integrallyformed with or fixedly secured to the substrate holder body on thesubstrate holding side, the retainer ring being arranged to surround anouter periphery of the substrate held by the substrate holder body sothat the retainer ring engages with the polishing surface radiallyoutside the substrate as the polishing of the substrate is effected. Thesubstrate holder body is provided on the substrate holding side with amembrane having opposite surfaces including inside and outside surfaces,the inside surface cooperating with a surface of the substrate holderbody to define a fluid pressure chamber to which a fluid pressure isapplied, the outer surface engaging with the substrate held by thesubstrate holder body.

In accordance with another aspect of the present invention, there isprovided a substrate holding apparatus in which, instead of the membranewhich covers the entire surface of the substrate, the apparatuscomprises a substrate support ring provided in the inner space andarranged to be sealingly engaged with the substrate to be held by thesubstrate holding apparatus, and a flexible seal member sealinglyconnected between the substrate support ring and the substrate holderbody so that a fluid pressure chamber is defined by the substrate holderbody, the flexible seal member and the substrate engaged with thesubstrate support ring. The fluid pressure chamber is arranged to beselectively connected to a pressurized fluid source or a vacuum source.

These substrate holding apparatuses eliminate a relative movementbetween the retainer ring and the wafer holder body whereby the behaviorof the retainer ring can be stabilized during polishing. A substrate isheld on the fluid pressure chamber so that the substrate can followundulations on a polishing surface.

In accordance with a further aspect of the present invention, there isprovided a polishing apparatus including a substrate holding apparatusas stated above.

Further, in accordance with another aspect of the present invention,there is provided a substrate polishing apparatus comprising a firstpolishing table having a hard polishing surface and a substrate holdingapparatus for holding a substrate and bringing it into contact with thehard polishing surface. The substrate holding apparatus comprises asubstrate holder body having a substrate holding side facing thepolishing surface and holding a substrate on the substrate holding sideand a membrane provided on the substrate holding side of the substrateholder body, the membrane having opposite surfaces including inside andoutside surfaces, the inside surface cooperating with a surface of thesubstrate holder body to define a fluid pressure chamber to which afluid pressure is applied, the outer surface engaging with the substrateheld by the substrate holder body. The hard polishing surface has, forexample, a modulus of compression of 19.6 MPa (200 kg/cm2) or more. Inthis apparatus, a substrate is held on the fluid pressure chamber whichis supplied with a fluid pressure to press the substrate against thepolishing surface so that the substrate can follow undulations on apolishing surface during its polishing operation.

The substrate polishing apparatus may further include a second polishingtable having a soft polishing surface which is softer (or of smallerelastic module) than the hard polishing of the first polishing table.The substrate holder body is arranged such that the substrate holderbody holds a substrate and, then, bring the substrate into contact withthe hard polishing surface to effect a first polishing of the substrateand, thereafter, bring the substrate into contact with the softpolishing surface to effect a second polishing of the substrate. By thisapparatus, a highly flattened wafer surface having fewer scratch markscan be obtained.

This polishing apparatus may be modified as follows. In stead of themembrane which covers the entire surface of the substrate, the apparatuscomprises a substrate support ring provided in the inner space andarranged to be sealingly engaged with the substrate to be held by thesubstrate holding apparatus, and a flexible seal member sealinglyconnected between the substrate support ring and the substrate holderbody so that a fluid pressure chamber is defined by the substrate holderbody, the flexible seal member and the substrate engaged with thesubstrate support ring. The fluid pressure chamber is arranged to beselectively connected to a pressurized fluid source or a vacuum source.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a substrate holding apparatusaccording to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing how the substrateholding apparatus of FIG. 1 is operated.

FIG. 3 is a longitudinal sectional view of a substrate holding apparatusaccording to a second embodiment of the present invention.

FIG. 4A is a bottom view of an example of a retainer ring having groovesformed on a lower surface thereof.

FIG. 4B is a cross-sectional view, taken along line A-A in FIG. 4A.

FIG. 5A is a bottom view of another example of a retainer ring havinggrooves formed on a lower surface thereof.

FIG. 5B is a cross-sectional view, taken along line A-A in FIG. 5A.

FIG. 6A is a bottom view of a further example of a retainer ring havinggrooves formed on a lower surface thereof.

FIG. 6B is a cross-sectional view, taken along line A-A in FIG. 6A.

FIG. 7 is a longitudinal sectional view of a substrate holding apparatusaccording to third embodiment of the present invention.

FIG. 8 is a schematic view showing an entire structure of a polishingapparatus including the substrate holding apparatus of FIGS. 1 to 3.

FIG. 9 is a longitudinal sectional view of a substrate holding apparatusaccording to a fourth embodiment of the present invention.

FIG. 10 is a bottom view of the substrate holding apparatus of FIG. 9.

FIG. 11 is a longitudinal sectional view showing how the substrateholding apparatus of FIG. 9 is operated.

FIG. 12 is a schematic view showing an entire structure of a polishingapparatus including the substrate holding apparatus of FIGS. 9 to 11.

FIG. 13 is a plan view of a polishing apparatus which is suitably usedfor two-stage polishing by using the substrate holding apparatus of thepresent invention.

FIG. 14 is a schematic illustration of a conventional substrate holdingapparatus in which a fluid pressure is applied to a wafer so as to pressthe wafer against a polishing surface, and the fluid pressure is alsoapplied to a retainer ring so as to press the retainer ring against thepolishing surface.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, description is made with regard to embodiments of thepresent invention, with reference to FIGS. 1 to 13.

FIG. 1 is a longitudinal sectional view of a substrate holding apparatus1 according to a first embodiment of the present invention. FIG. 2 is alongitudinal sectional view showing how the substrate holding apparatusof FIG. 1 is operated.

The substrate holding apparatus 1 is adapted to hold a substrate or, inthis embodiment, a semiconductor wafer W to be polished and press thewafer against a polishing surface of a polishing table. As shown in FIG.1, the substrate holding apparatus comprises a dish-like wafer holderbody 2 defining an inner space and a retainer ring 3 fixed to the waferholder body 2. The wafer holder body 2 is made of a material having highstrength and high rigidity, such as a metal and a ceramic, and comprisesa circular upper plate 2A and a circumferential wall portion 2Bextending downward from the upper plate 2A. The retainer ring 3 is fixedto a lower end of the circumferential wall portion 2B. The retainer ring3 is made of a resin material having high rigidity. It should be notedthat the retainer ring 3 may be formed integrally with the wafer holderbody 2.

The wafer holder body 2 and the retainer ring 3 define an inner spacefor containing an elastic membrane 4 and an elastic membrane supportingmember 5 in a generally cylindrical form. The elastic membranesupporting member 5 holds an outer circumferential portion of theelastic membrane 4. A flexible sheet 6 made of an elastic membraneextends between the elastic membrane supporting member 5 and the waferholder body 2. A fluid chamber 8 having a sealable structure is formedby the wafer holder body 2, the elastic membrane 4, the flexible sheet 6and an inner surface of the wafer holder body. Each of the elasticmembrane 4 and the flexible sheet 6 is formed from a rubber materialwhich is excellent in strength and durability, such as an ethylenepropylene rubber (EPDM), a polyurethane rubber or a silicone rubber. Apressurized fluid such as pressurized air is supplied to the fluidchamber 8 through a fluid passage 10 comprising a tube and a connector.The pressure of pressurized fluid supplied to the fluid chamber 8 can bevaried by means of a regulator. A slight gap is formed between an outercircumferential surface of the elastic membrane 4, and the wafer holderbody 2 and the retainer ring 3. The elastic membrane 4 and the elasticmembrane supporting member 5 are vertically movable relative to thewafer holder body 2 and the retainer ring 3.

For insuring high polishing performance, it is preferred to form thefluid chamber 8 by using an elastic membrane as in this embodiment.However, the elastic membrane 4 may not be used and the wafer may bepressed by direct contact with the fluid. When the elastic membrane 4 isnot used, the fluid chamber is formed by the wafer holder body 2 and therear surface of the wafer to be polished.

An annular stopper plate 13 is fixed through a support member 12 to theupper plate 2A of the wafer holder body 2. An upper end surface 13 a ofthe stopper plate 13 is positioned at a predetermined height and thestopper plate 13 provides a restricting member. When the pressurizedfluid is supplied to the fluid chamber 8, the elastic membrane 4 and theelastic membrane supporting member 5 move as a unit downward relative tothe wafer holder body 2. In this instance, an upper end portion 5 a ofthe elastic membrane supporting member 5 engages the upper end surface13 a of the stopper plate 13, thus limiting the downward movement of theelastic membrane 4 and the elastic membrane supporting member 5 to apredetermined range.

A chucking plate 14 including a plurality of through-holes 14 h isprovided inside the elastic membrane supporting member 5. In thisembodiment, the chucking plate 14 is fixed to an inner side of theelastic membrane supporting member 5. However, the chucking plate 14 maybe formed integrally with the elastic membrane supporting member 5. Anumber of spherical recesses 14 a are formed on a lower surface of thechucking plate 14. As shown in FIG. 2, when a negative pressure isapplied to the fluid chamber 8 through the fluid passage 10 from avacuum source, the elastic membrane 4 is deformed along the sphericalrecesses 14 a of the chucking plate 14. That is, the portions of theelastic membrane 4 corresponding to the spherical recesses 14 a of thechucking plate 14 form suction cups and hold the wafer W on a lowersurface of the elastic membrane 4.

A plurality of stoppers 17 operated by actuators 16 such as aircylinders is provided in the upper plate 2A of the wafer holder body 2.By operating the actuators 16, the stoppers 17 are protruded downward bya predetermined length as shown in FIG. 2. When a negative pressure isapplied to the fluid chamber 8, the elastic membrane supporting member 5moves upward together with the elastic membrane 4 and the upper endportion 5 a of the elastic membrane supporting member 5 abuts againstthe stoppers 17, thus limiting the upward movement of the elasticmembrane supporting member 5 and the elastic membrane 4 to apredetermined range. That is, the stoppers 17 provide restrictingmembers having an adjustable heightwise position. When the actuator 16is arranged so as to have a mechanism such as an air cylinder capable ofgenerating a variable pressure and the stoppers 17 are protruded duringpolishing so as to press the elastic membrane supporting member 5 in adownward direction, an outer circumferential portion of the wafer W canbe mechanically pressed against the polishing surface. A wafer holderdrive shaft 18 is provided above the upper plate 2A of the wafer holderbody 2. The drive shaft 18 and the wafer holder body 2 are connectedthrough a universal joint 19.

The universal joint 19 transmits pressure and torque of the drive shaft18 to the wafer holder body 2 while permitting inclination of the driveshaft 18 and the wafer holder body 2 relative to each other. Theuniversal joint 19 comprises a spherical bearing mechanism which permitsinclination of the wafer holder body 2 and the drive shaft 18 relativeto each other and a torque transmitting mechanism which transmitsrotation of the drive shaft 18 to the wafer holder body 2. The sphericalbearing mechanism comprises a spherical recess 18 a formed at a centralportion of a lower surface of the drive shaft 18, a spherical recess 2 aformed at a central portion of an upper surface of the upper plate 2Aand a bearing ball 21 made of a material having high hardness, such as aceramic, provided between the spherical recess 18 a and the sphericalrecess 2 a.

The torque transmitting mechanism comprises a drive pin (not shown)fixed to the drive shaft 18 and a driven pin (not shown) fixed to theupper plate 2A. The two pins are capable of moving vertically relativeto each other and engaging at different contact positions. Therefore, atorque of the drive shaft 18 is surely transmitted to the wafer holderbody 2 even when the wafer holder body 2 is inclined.

Next, explanation is made with regard to operation of the wafer holder 1arranged as mentioned above.

The wafer holder 1 as a whole is moved to a position for transferring awafer and the fluid chamber 8 is connected to the vacuum source throughthe fluid passage 10. Consequently, as shown in FIG. 2, the elasticmembrane 4 is deformed and holds the wafer W on the lower surfacethereof due to the effect of suction cups formed along the recesses 14 aof the chucking plate 14. While holding the wafer W on the elasticmembrane 4, the wafer holder 1 as a whole is moved to a position above apolishing table (designated by reference numeral 30 in FIG. 8) having apolishing surface (such as a polishing pad). The wafer W and theretainer ring 3 are then pressed against the polishing surface tothereby start polishing. An outer circumferential edge of the wafer W isheld by the retainer ring 3 so that the wafer W is not separated fromthe wafer holder 1.

For polishing the wafer W, an air cylinder (designated by referencenumeral 33 in FIG. 8) connected to the drive shaft 18 is operated tothereby press the retainer ring 3 fixed to the wafer holder body 2against the polishing surface of the polishing table under apredetermined pressure. In this state, the pressurized fluid is suppliedunder a predetermined pressure to the fluid chamber 8 to thereby pressthe wafer W against the polishing surface of the polishing table. Thepressure applied to the wafer W for polishing is adjusted to a desiredlevel by controlling the pressure of pressurized fluid supplied to thefluid chamber 8. Thus, the pressure of fluid in the fluid chamber 8 isapplied to the wafer W, so that it is possible to obtain a uniformpressure distribution for polishing across an entire surface of thewafer W from the center to the circumferential edge thereof, regardlessof the thickness of the wafer W. This enables uniform polishing of theentire surface of the wafer W.

During polishing, pressure substantially equal to or slightly higherthan that applied to the wafer W is applied to the retainer ring 3through the air cylinder, so that the polishing surface outside thewafer W is pressed under a pressure substantially equal to that of thewafer W. Therefore, a uniform pressure distribution can be obtainedcontinuously across an area from the center of the wafer W to an outercircumferential portion of the retainer ring 3 outside the wafer W.Therefore, excessive or insufficient polishing at the circumferentialedge of the wafer W can be prevented.

FIG. 3 is a vertical cross-sectional view of a substrate holdingapparatus according to a second embodiment of the present invention. Inthis embodiment, the chucking plate 14 is not provided and a spaceinside the elastic membrane supporting member 5 is empty. Instead ofproviding the chucking plate 14, a plurality of through-holes 4 h isformed in the elastic membrane 4 in an area between the center and anouter circumferential portion thereof. Therefore, when a negativepressure is applied from the vacuum source through the fluid passage 10to the fluid chamber 8 for holding the wafer W on the lower surface ofthe elastic membrane 4, the wafer W is held due to the effect of vacuumforce directly applied through the through-holes 4 h.

In the wafer holder 1 in this embodiment, during polishing, as is in thefirst embodiment, a pressurized fluid is supplied to the fluid chamber 8so that a wafer W is pressed against a polishing surface by the elasticmembrane 4 with the through-holes 4 h in the membrane 4 being closed bythe wafer W.

In the embodiments shown in FIGS. 1 to 3, the retainer ring 3 is fixedlyconnected to the wafer holder body 2 having a rigid construction and theretainer ring 3 is vertically moved by vertically moving the waferholder body 2. By this arrangement, the pressure applied to the waferholder body 2 can be utilized as a pressure for pressing the retainerring 3. Further, because the retainer ring 3 is fixed to the waferholder body 2, undesirable lateral (or radial) movement of the retainerring 3 can be prevented. Therefore, the distance between the retainerring 3 and the circumferential edge of the wafer can be constantlyminimized, and uniformity and stability in the polishing of the outercircumferential portion of the wafer W can be ensured.

Since the retainer ring 3 is fixedly connected to the wafer holder body2, the retainer ring can be imparted with high rigidity and the behaviorof the retainer ring during polishing can be stabilized. The waferholding pressurizing mechanism of a floating type structure followsundulations in the polishing surface inside the retainer ring which isstable and has high rigidity. Consequently, the behavior of the retainerring can be stabilized, even on a hard polishing surface, to therebyachieve excellent stability of the polishing of the wafer.

By adjustably positioning the stoppers 17, upward movement of theelastic membrane supporting member 5 is restricted at a predeterminedheight, thus limiting upward movement of the chucking plate 14 to apredetermined range. This prevents warpage of the wafer held on theelastic membrane 4 and a lowering of product quality such as breakage ofthe wafer. Further, by protruding the stoppers 17 by using the cylindermechanism and pressing the elastic membrane supporting member 5 downwardduring polishing, the pressure for pressing the wafer W against thepolishing surface can be varied on a part of the wafer surface, thusmaking it possible to obtain desired polishing properties in relation tothe profile of the surface to be polished.

In the wafer holder shown in FIG. 3, in which the through-holes 4 h areformed in the elastic membrane 4, the elastic membrane 4 directly holdsthe wafer W due to the effect of vacuum force applied through thethrough-holes 4 h. Therefore, there is no problem of a change inproperties of the elastic membrane 4 due to contact with the chuckingplate 14 shown in FIG. 1. This enhances stability of uniform polishingof the wafer. Further, for holding the wafer W, it is unnecessary toutilize the effect of a suction cup formed by using the chucking plate14. Therefore, there is no need to provide the chucking plate 14 andonly the elastic membrane supporting member 5 in an annular form isnecessary.

FIGS. 4A to 6B show examples of retainer rings having grooves formed onlower surfaces thereof. FIG. 4A, FIG. 5A and FIG. 6A are bottom views ofthe retainer rings. FIG. 4B, FIG. 5B and FIG. 6B are cross-sectionalviews, taken along lines A-A in FIG. 4A, FIG. 5A and FIG. 6A,respectively.

In the example of FIGS. 4A and 4B, a plurality of radial grooves 3 g-1(each extending in a radial direction indicated by an arrow r) is formedon the lower surface of the retainer ring 3.

In the example of FIGS. 5A and 5B, a plurality of grooves 3 g-2 inclinedat a predetermined angle □ relative to the radial direction r is formedon the lower surface of the retainer ring 3.

In the example of FIGS. 6A and 6B, a plurality of radial grooves 3 g-3(each extending in the radial direction r) is formed on the lowersurface of the retainer ring 3. The radial grooves 3 g-3 extend from anouter circumferential edge of the retainer ring 3 to an intermediateposition at a slight distance from an inner circumferential edge of theretainer ring.

Because the retainer ring presses the polishing surface (such as apolishing pad) outside the wafer, when the entire lower surface of theretainer ring is flat, the abrasive liquid (slurry) might not smoothlyflow into an area inside the retainer ring. That is, the amount ofabrasive liquid supplied to the wafer becomes insufficient, leading to alowering of uniformity in the polishing of the wafer and a lowering of arate of polishing. Further, the wafer and the polishing surface aresubject to high friction, leading to a problem, namely a high power loadon the polishing apparatus.

As a countermeasure, it is considered to reduce the width of the lowersurface of the retainer ring so as to minimize the effect of theretainer ring of disturbing the inflow of abrasive liquid. In this case,however, the flat portion of the lower surface of the retainer ring isreduced in area due to non-uniform wear of the lower surface of theretainer ring, making it difficult for the retainer ring to press thepolishing surface in a stable manner. Further, the amount of wear of theretainer ring becomes large, thereby reducing the life of the retainerring.

In the present invention, as shown in FIGS. 4A and 4B, the grooves 3 g-1may be formed on the lower surface of the retainer ring 3 which isbrought into contact with the polishing surface. By this arrangement,the abrasive liquid smoothly flows into an area inside the retainer ring3 to thereby secure the supply of abrasive liquid to the wafer, thuspreventing a lowering of uniformity in the polishing of the wafer and alowering of a rate of polishing. As shown in FIGS. 5A and 5B, thegrooves 3 g-2 inclined relative to the radial direction may be formed onthe lower surface of the retainer ring. The direction of inclination ofthe grooves 3 g-2 corresponds to a rotation direction R of the retainerring 3. This enhances smooth flow of the abrasive liquid to the wafer.However, when there is a high possibility of accelerating polishing on apart of the wafer due to oversupply of the abrasive liquid, the grooves3 g-3 in FIGS. 6A and 6B may be formed on the lower surface of theretainer ring. The grooves 3 g-3 do not extend to the innercircumferential edge of the retainer ring 3, so as to leave a wallportion for preventing oversupply of the abrasive liquid, therebypreventing excessive polishing of a part of the wafer while securing thesupply of abrasive liquid to the wafer inside the retainer ring.

Another advantage of the grooves 3 g-3 is explained below. When thegrooves extend to the inner circumferential edge of the retainer ring,the following problems arise. That is, when relative rotation betweenthe wafer holder and the wafer occurs, an angular portion of the outercircumferential surface of the wafer, which is formed by forming anorientation flat or a notch in the wafer, makes contact with the grooveof the retainer ring. Consequently, a portion around the groove at theinner circumferential edge of the retainer ring is likely to become worndue to impact. The orientation flat is especially liable to cause such awear. Further, pronounced noise is even generated due to impact when theorientation flat makes contact with the groove. The wear at the grooveof the retainer ring can be prevented by leaving a wall portion at aterminal end of the groove of the retainer ring as shown in FIGS. 6A and6B.

The formation of grooves on the lower surface of the retainer ring canbe applied to not only wafer holders such as those shown in FIGS. 1 to3, but also various wafer holders as long as they are capable ofpressing the retainer ring against the polishing surface. FIG. 7 showsan illustrative example of a wafer holder other than that shown in FIGS.1 to 3.

In the example of FIG. 7, a wafer holder 101 comprises a wafer holderbody 102 and a holding plate 103 for holding an upper surface of asubstrate to be polished, such as a semiconductor wafer W. The holdingplate 103 is made of a material having high rigidity, such as a ceramic,and has a wafer holding surface 103 a which is adapted so as not to bedeformed. An elastic mat 106 is adhered to a lower surface of theholding plate 103.

In order to hold the wafer W on the lower surface of the holding plate103, a retainer ring (or guide ring) 107 for holding an outercircumferential surface of the wafer W is provided on an outercircumferential surface of the wafer holder 101. A chamber C is formedbetween the holding plate 103 and the wafer holder body 102. The chamberC is used for applying a fluid pressure through communication holes 103m formed in the holding plate 103 to a back side of the wafer W. Byevacuating the chamber C by means of a vacuum pump, the wafer W can beheld on the wafer holding surface 103 a due to the effect of vacuumforce. It should be noted that for separating the wafer W from the waferholding surface 103 a of the holding plate 103, a liquid such as purewater is supplied to the chamber C.

In the example of FIG. 7, a wafer held on the lower surface of the waferholder is pressed against the polishing surface by an air cylinder formoving the wafer holder drive shaft 18 in a vertical direction. Theretainer ring 107 having grooves 103 g-3 formed on a lower surfacethereof is disposed so that it surrounds the wafer. The retainer ring107 is independently pressed against the polishing surface due to theeffect of pressure of a pressurized fluid supplied to a space 143. Thespace 143 is defined by a lower seal ring 140A and an upper seal ring140B. The upper seal ring 140B comprises a ring 141 b fixed to amounting flange portion 102 a of the wafer holder body 102 and lip seals142 b for sealing spaces between the ring 141 b and a mounting flangeportion 102 a of the wafer holder body 102. The lower seal ring 140Acomprises a ring 141 a for pressing the retainer ring 107 and lip seals142 a provided radially inside and outside the retainer ring 141 a forsealing spaces between the ring 141 a and the mounting flange portion102 a of the wafer holder body 102. The retainer ring 107 comprises afirst retainer ring member 107 a which is vertically movable and asecond retainer ring member 107 b fixed to the wafer holder body 102. Inthe embodiment of FIG. 7, even when the retainer ring 107 is worn, theretainer ring can be pressed under a desired pressure. The grooves 103g-3 formed in the retainer ring 107 are of the same type as the grooves3 g-3 in FIGS. 6A and 6B. That is, the grooves 103 g-3 extend from theradially outer peripheral edge of the retainer ring and short of theradially inner peripheral edge of the same. The effects of the grooves103 g-3 are the same as those described above in connection with thegrooves 3 g-3. The grooves 103 g-3 may be inclined at a predeterminedangle (□) relative to the radial direction r, as shown in FIG. 5A.

FIG. 8 is a cross-sectional view showing an entire structure of apolishing apparatus including the substrate holding apparatus of FIGS. 1to 3. As shown in FIG. 8, the polishing table 30 has a polishing pad 31attached to an upper surface thereof and is provided below the waferholder 1.

The wafer holder 1 is connected to the drive shaft 18 through theuniversal joint 19. The drive shaft 18 is connected to the air cylinder33 fixed to a wafer holder head 32. The drive shaft 18 is verticallymoved by means of the air cylinder 33, thereby moving the wafer holder 1as a whole in a vertical direction and pressing the retainer ring 3fixed to the wafer holder body 2 against the polishing table 30.

The drive shaft 18 is connected to a rotary cylinder 34 through a key(not shown). The rotary cylinder 34 has a timing pulley 35 on an outercircumferential surface thereof. The timing pulley 35 is connectedthrough a timing belt 36 to a timing pulley 38 which is connected to awafer holder motor 37 fixed to the wafer holder head 32. Therefore, therotary cylinder 34 and the drive shaft 18 are rotated as a unit by thewafer holder motor 37 through the timing pulley 38, the timing belt 36and the timing pulley 35 to thereby rotate the wafer holder 1. The waferholder head 32 is supported by a wafer holder head shaft 39 fixedlysupported by a frame (not shown).

The air cylinder 33 and the fluid chamber 8 are, respectively, connectedthrough a regulator R1 and a regulator R2 to a pressurized air source24. The pressure of pressurized air supplied to the air cylinder 33 iscontrolled by the regulator R1, to thereby adjust the pressure forpressing the retainer ring 3 against the polishing pad 31. The pressureof pressurized air supplied to the fluid chamber 8 is controlled by theregulator R2, to thereby adjust the pressure for pressing the wafer Wagainst the polishing pad 31.

An abrasive liquid supply nozzle 40 is provided above the polishingtable 30. An abrasive liquid Q is supplied onto the polishing pad 31 onthe polishing table 30 through the abrasive liquid supply nozzle 40.

In this polishing apparatus, for polishing, while holding the wafer W onthe lower surface of the elastic membrane 4 of the wafer holder 1, theair cylinder 33 is operated to thereby press the retainer ring 3 fixedto the wafer holder body 2 toward the polishing table 30, andpressurized air is supplied to the fluid chamber 8 to thereby press thewafer W against the polishing pad 31 on the polishing table 30, which isrotating. On the other hand, the abrasive liquid Q is supplied from theabrasive liquid supply nozzle 40 so as to retain the abrasive liquid Qon the polishing pad 31. Thus, polishing is conducted while retainingthe abrasive liquid Q between the wafer surface to be polished (a lowersurface of the wafer W) and the polishing pad 31.

For polishing, the pressure for pressing the retainer ring 3 against thepolishing pad 31, which is applied through the air cylinder 33, and thepressure for pressing the wafer W against the polishing pad 31, which isapplied by means of pressurized air supplied to the fluid chamber 8, areadjusted to a desired level. During polishing, the pressure for pressingthe retainer ring 3 against the polishing pad 31 can be varied by meansof the regulator R1, and the pressure for pressing the wafer W againstthe polishing pad 31 can be varied by means of the regulator R2.Consequently, during polishing, by controlling the pressure for pressingthe retainer ring 3 against the polishing pad 31 and the pressure forpressing the wafer W against the polishing pad 31, a uniform pressuredistribution can be obtained continuously across an area from the centerof the wafer W to an outer circumferential portion of the retainer ring3 outside the wafer W. Therefore, excessive or insufficient polishing atthe circumferential edge of the wafer W can be prevented.

In the present invention, the polishing surface formed on the polishingtable may be prepared by a polishing pad such as that described above oran abrasive plate comprising fixed abrasive particles. As the polishingpad, various commercially available polishing pads, for example,SUBA800, IC-1000 and IC-1000/SUBA400 (a two-layered cloth) manufacturedand sold by Rodel, Inc., and Surfin xxx-5 and Surfin 000 manufacturedand sold by FUJIMI INCORPORATED can be used. The SUBA800, Surfin xxx-5and Surfin 000 are non-woven cloths which comprise fibers bound by usinga urethane resin. The IC-1000 comprises a single layer of hard, foamedpolyurethane, which has a porous structure and includes a number of finerecesses or holes formed on a surface thereof.

The abrasive plate comprises fixed abrasive particles which are bound byusing a binder and formed into a plate. Polishing is conducted byutilizing the abrasive particles freed from the abrasive plate. Theabrasive plate comprises the abrasive particles, the binder and pores.Examples of abrasive particles include particles of cerium oxide (CeO2)having an average particle diameter of 0.5 □m or less. As the binder,for example, an epoxy resin is used. The abrasive plate provides a hardpolishing surface. The abrasive plate may have a two-layered structurecomprising a thin layer of fixed abrasive particles and an elasticpolishing pad adhered to a lower side of the fixed abrasive particles.The above-mentioned IC-1000 also provides a hard polishing surface.

The wafer holder of the present invention is suitable for use with apolishing member having a hard polishing surface, especially suitablefor a polishing surface having a modulus of elasticity of compression of19.6 MPa (200 kg/cm2) or more.

In a conventional wafer holder, a wafer is held on a backing padprovided on a rigid wafer holder body. Because the polishing pad iselastic, shocks on the wafer are absorbed by the polishing pad. However,when a hard polishing surface is used, undulation on the polishingsurface is transferred to and affects the wafer surface to be polished.Further, a mark corresponding to a vacuum opening of the backing pad isformed on a rear surface of the wafer.

On the other hand, in the wafer holder of the present invention in whicha wafer is held on an elastic membrane by utilizing fluid pressure,shocks on the wafer due to a hard, undulating polishing surface can beabsorbed by the fluid pressure acting on the rear surface of the wafer.Thus, even when the polishing surface is hard, high polishingperformance can be maintained and no mark corresponding to the vacuumopening is formed on the wafer.

Further, in the present invention, since the retainer ring is fixedlyconnected to the wafer holder body, the retainer ring can be impartedwith high rigidity and unstable movement of the retainer ring can besuppressed, thereby stabilizing polishing performance.

FIG. 9 is a longitudinal sectional view of a substrate holding apparatus1 according to another embodiment of the present invention. FIG. 10 is abottom view of the substrate holding apparatus of FIG. 9. FIG. 11 is asectional view showing how the substrate holding apparatus of FIG. 9 isoperated.

The substrate holding apparatus 1 is adapted to hold a substrate to bepolished, such as a semiconductor wafer, and press the wafer against apolishing surface of a polishing table. As shown in FIG. 9, thesubstrate holding apparatus of this embodiment comprises a dish-likewafer holder body 2 defining an inner space and a retainer ring 3 fixedto a lower end of the wafer holder body 2. The wafer holder body 2 ismade of a material having high strength and high rigidity, such as ametal and a ceramic, and comprises a circular upper plate 2A and acircumferential wall portion 2B extending downward from the upper plate2A. The retainer ring 3 is fixed to a lower end of the circumferentialwall portion 2B. The retainer ring 3 is made of a resin material havinghigh rigidity. It should be noted that the retainer ring 3 may be formedintegrally with the wafer holder body 2.

The wafer holder body 2 and the retainer ring 3 define an inner spacefor containing an elastic membrane 4 and an elastic membrane supportingmember 5 in a generally disk-like form. The elastic membrane supportingmember 5 holds an outer circumferential portion of the elastic membrane4. A flexible sheet 6 made of an elastic membrane extends between theelastic membrane supporting member 5 and the wafer holder body 2. Afluid chamber 8 is formed by the wafer holder body 2, the elasticmembrane 4, the flexible sheet 6 and an inner surface of the waferholder body 2. Each of the elastic membrane 4 and the flexible sheet 6is formed from a rubber material which is excellent in strength anddurability, such as an ethylene propylene rubber (EPDM), a polyurethanerubber or a silicone rubber. A pressurized fluid such as pressurized airis supplied to the fluid chamber 8 through a fluid passage 10 comprisinga tube and a connector. The pressurized fluid supplied to the fluidchamber 8 flows through through-holes 5 h formed in the elastic membranesupporting member 5 to a rear surface of the elastic membrane 4, thusapplying the pressure of pressurized fluid to the rear surface of theelastic membrane 4. The pressure of pressurized fluid supplied to thefluid chamber 8 can be varied by means of a regulator. A slight gap isformed between an outer circumferential surface of the elastic membrane4 and the wafer holder body 2 and the retainer ring 3. The elasticmembrane 4 and the elastic membrane supporting member 5 are verticallymovable relative to the wafer holder body 2 and the retainer ring 3.

For insuring high polishing performance, it is preferred to form thefluid chamber 8 by using an elastic membrane as in this embodiment.However, the elastic membrane 4 may not be used so that the wafer may bepressed by direct contact with the fluid. When the elastic membrane 4 isnot used, the fluid chamber is formed by the wafer holder body 2 and therear surface of the wafer to be polished.

An annular stopper plate 13 is fixed through a support member 12 to theupper plate 2A of the wafer holder body 2. An upper end surface 13 a ofthe stopper plate 13 is positioned at a predetermined height and thestopper plate 13 provides a restricting member. When the pressurizedfluid is supplied to the fluid chamber 8, the elastic membrane 4 and theelastic membrane supporting member 5 move as a unit downward relative tothe wafer holder body 2. In this instance, an upper end portion 5 a ofthe elastic membrane supporting member 5 engages the upper end surface13 a of the stopper plate 13, thus limiting the downward movement of theelastic membrane 4 and the elastic membrane supporting member 5 to apredetermined range. The elastic membrane 4 includes a plurality ofopenings 4 a formed therein. Vacuum portions 14 each having acommunication hole 14 h are exposed from the respective openings 4 a.The vacuum portions 14 are formed at a central portion of the elasticmembrane supporting member 5. In this embodiment, the vacuum portions 14are formed integrally with the elastic membrane supporting member 5.However, the elastic membrane supporting member 5 may be formed into anannular form and a disk-like chucking plate including a plurality ofvacuum portions 14 may be employed so that the chucking plate is fixedto an inner side of the elastic membrane supporting member 5.

As shown in FIG. 10, five openings 4 a are formed at a central portionof the elastic membrane 4, and the vacuum portions 14 are exposed fromthe respective openings 4 a. As shown in FIG. 9, a lower end of thecommunication hole 14 h of each vacuum portion 14 is open. All thecommunication holes 14 h join inside the elastic membrane supportingmember 5 and are connected through a tube 11 in the fluid chamber 8 to avacuum source. When a negative pressure is applied to the open ends ofthe communication holes 14 h through the vacuum source, a semiconductorwafer W is held on the vacuum portions 14 under vacuum force. As shownin FIG. 9, during polishing, the vacuum portions 14 are located inwardof a lower end surface of the elastic membrane 4 and do not protrudefrom the lower end surface of the elastic membrane 4. When the wafer Wis held under vacuum force, as shown in FIG. 11, lower end surfaces ofthe vacuum portions 14 become substantially flush with the lower endsurface of the elastic membrane 4. An elastic sheet 15 such as a thinrubber sheet is attached to the lower end surface of each vacuum portion14 so that the vacuum force is applied to the wafer through the thinrubber sheet.

A wafer holder drive shaft 18 is provided above the upper plate 2A ofthe wafer holder body 2. The drive shaft 18 and the wafer holder body 2are connected through a universal joint 19. The universal joint 19transmits pressure and torque of the drive shaft 18 to the wafer holderbody 2 while permitting inclination of the drive shaft 18 and the waferholder body 2 relative to each other. The universal joint 19 comprises aspherical bearing mechanism which permits inclination of the waferholder body 2 and the drive shaft 18 relative to each other and a torquetransmitting mechanism which transmits rotation of the drive shaft 18 tothe wafer holder body 2. The spherical bearing mechanism comprises aspherical recess 18 a formed at a central portion of a lower surface ofthe drive shaft 18, a spherical recess 2 a formed at a central portionof an upper surface of the upper plate 2A and a bearing ball 21 made ofa material having high hardness, such as a ceramic, provided between thespherical recess 18 a and the spherical recess 2 a.

The torque transmitting mechanism comprises a drive pin (not shown)fixed to the drive shaft 18 and a driven pin (not shown) fixed to theupper plate 2A. The two pins are capable of moving vertically relativeto each other and engaging at different contact positions. Therefore, atorque of the drive shaft 18 is surely transmitted to the wafer holderbody 2 even when the wafer holder body 2 is inclined.

Next, explanation is made with regard to operation of the wafer holder 1explained with reference to FIGS. 9-11.

The wafer holder 1 as a whole is moved to a position for transferring awafer and the communication holes 14 h of the vacuum portions 14 areconnected to the vacuum source through the tube 11. Consequently, asshown in FIG. 11, the wafer W is held on the lower end surfaces of thevacuum portions 14 due to the effect of vacuum force applied through thecommunication holes 14 h. In this instance, a slight positive pressureis applied to the fluid chamber 8 so as to prevent upward movement ofthe elastic membrane supporting member 5 and the vacuum portions 14, andthe upper end portion 5 a of the elastic membrane supporting member 5engages the upper end surface 13 a of the stopper plate 13 to therebyhold the elastic membrane supporting member 5 and the vacuum portions 14at a predetermined position. While holding the wafer W under vacuumforce, the wafer holder 1 is moved to a position above a polishing table(designated by reference numeral 30 in FIG. 12) having a polishingsurface (such as a polishing pad). The wafer W and the retainer ring 3are then pressed against the polishing surface to thereby startpolishing. An outer circumferential edge of the wafer W is held by theretainer ring 3 so that the wafer W is not separated from the waferholder 1.

For polishing the wafer W, an air cylinder (designated by referencenumeral 33 in FIG. 12) connected to the drive shaft 18 is operated, tothereby press the retainer ring 3 fixed to the wafer holder body 2against the polishing surface of the polishing table under apredetermined pressure. In this state, the pressurized fluid is suppliedunder a predetermined pressure to the fluid chamber 8, to thereby pressthe wafer W against the polishing surface of the polishing table. Thepressure applied to the wafer W for polishing is adjusted to a desiredlevel by controlling the pressure of pressurized fluid supplied to thefluid chamber 8. Thus, the fluid pressure is directly applied to thewafer W at its portion corresponding to the opening 4 a, while the fluidpressure is indirectly applied to the remaining portion of the wafer Wthrough the elastic membrane 4. However, the pressures applied to thesetwo portions of the wafer W are equal. That is, since the pressure offluid in the fluid chamber 8 is applied to an entire surface of thewafer W, it is possible to obtain a uniform pressure distribution forpolishing across an entire surface of the wafer W from the center to thecircumferential edge thereof, regardless of the thickness of the waferW. This enables uniform polishing of the entire surface of the wafer W.During polishing, the elastic membrane 4 is in intimate contact with therear surface of the wafer W around the openings 4 a, so that there issubstantially no leakage of the pressurized fluid from the fluid chamber8 to the outside.

During polishing, pressure substantially equal to or slightly higherthan that applied to the wafer W is applied to the retainer ring 3through the air cylinder, so that the polishing surface outside thewafer W is pressed under a pressure substantially equal to that of thewafer W. Therefore, a uniform pressure distribution can be obtainedcontinuously across an area from the center of the wafer W to an outercircumferential portion of the retainer ring 3 outside the wafer W.Therefore, excessive or insufficient polishing at the circumferentialedge of the wafer W can be prevented.

In the wafer holder shown in FIGS. 9 to 11, the retainer ring 3 isfixedly connected to the wafer holder body 2 having a rigid constructionand the retainer ring 3 is vertically moved by vertically moving thewafer holder body 2. By this arrangement, the pressure applied to thewafer holder body 2 can be utilized as a pressure for pressing theretainer ring 3. Further, because the retainer ring 3 is fixed to thewafer holder body 2, undesirable lateral (or radial) movement of theretainer ring 3 can be prevented. Therefore, the distance between theretainer ring 3 and the circumferential edge of the wafer surface can beconstantly minimized, and uniformity and stability in the polishing ofthe outer circumferential portion of the wafer W can be ensured.

Since the retainer ring 3 is fixedly connected to the wafer holder body2, the retainer ring can be imparted with high rigidity and the behaviorof the retainer ring during polishing can be stabilized. The waferholding pressurizing mechanism of a floating type structure followsundulation of the polishing surface inside the retainer ring which isstable and has high rigidity. Consequently, the behavior of the retainerring can be stabilized even on a hard polishing surface to therebyachieve excellent stability of the polishing of the wafer.

The openings 4 a are formed in the elastic membrane 4 and the vacuumportions 14 having the communication holes 14 h are provided in theopenings 4 a. The wafer W is held due to the effect of vacuum forceapplied through the communication holes 14 h connected to the vacuumsource. That is, the vacuum portions 14 directly hold the wafer W due tothe effect of vacuum force. Therefore, there is no need to impart theelastic membrane 4 with a suction cup-like configuration. Therefore, achange in properties of the elastic membrane 4 is unlikely to occur sothat uniformity in the polishing of wafers can be stably maintained.

FIG. 12 is a cross-sectional view showing an entire structure of apolishing apparatus including the substrate holding apparatus of FIGS. 9to 10. As shown in FIG. 12, the polishing table 30 has a polishing pad31 attached to an upper surface thereof and is provided below the waferholder 1.

The wafer holder 1 is connected to the drive shaft 18 through theuniversal joint 19. The drive shaft 18 is connected to the air cylinder33 fixed to a wafer holder head 32. The drive shaft 18 is verticallymoved by means of the air cylinder 33, thereby moving the wafer holder 1as a whole in a vertical direction and pressing the retainer ring 3fixed to the wafer holder body 2 against the polishing table 30.

The drive shaft 18 is connected to a rotary cylinder 34 through a key(not shown). The rotary cylinder 34 has a timing pulley 35 on an outercircumferential surface thereof. The timing pulley 35 is connectedthrough a timing belt 36 to a timing pulley 38 which is connected to awafer holder motor 37 fixed to the wafer holder head 32. Therefore, therotary cylinder 34 and the drive shaft 18 are rotated as a unit by thewafer holder motor 37 through the timing pulley 38, the timing belt 36and the timing pulley 35 to thereby rotate the wafer holder 1. The waferholder head 32 is supported by a wafer holder head shaft 39 fixedlysupported by a frame (not shown).

The air cylinder 33 and the fluid chamber 8 are, respectively, connectedthrough a regulator R1 and a regulator R2 to a pressurized air source24. The pressure of pressurized air supplied to the air cylinder 33 iscontrolled by the regulator R1 to thereby adjust the pressure forpressing the retainer ring 3 against the polishing pad 31. The pressureof pressurized air supplied to the fluid chamber 8 is controlled by theregulator R2 to thereby adjust the pressure for pressing the wafer Wagainst the polishing pad 31. The communication holes 14 h of the vacuumportions 14 are connected through a valve V to a vacuum source 25 suchas a vacuum pump.

An abrasive liquid supply nozzle 40 is provided above the polishingtable 30. An abrasive liquid Q is supplied onto the polishing pad 31 onthe polishing table 30 through the abrasive liquid supply nozzle 40.

In this polishing apparatus, for transferring the wafer W, thecommunication holes 14 h of the vacuum portions 14 are communicated withthe vacuum source 25 to thereby apply a vacuum force to the wafer W forholding the wafer W on the vacuum portions 14. For polishing, the vacuumforce applied to the wafer W through the vacuum portions 14 is releasedand, while holding the wafer W on the lower end surface of the elasticmembrane 4 of the wafer holder 1, the air cylinder 33 is operated tothereby press the retainer ring 3 fixed to the wafer holder body 2toward the polishing table 30, and pressurized air is supplied to thefluid chamber 8, to thereby press the wafer W against the polishing pad31 on the polishing table 30, which is rotating. On the other hand, theabrasive liquid Q is supplied from the abrasive liquid supply nozzle 40so as to retain the abrasive liquid Q on the polishing pad 31. Thus,polishing is conducted while retaining the abrasive liquid Q between thewafer surface to be polished (a lower surface of the wafer W) and thepolishing pad 31.

For polishing, the pressure for pressing the retainer ring 3 against thepolishing pad 31, which is applied through the air cylinder 33, and thepressure for pressing the wafer W against the polishing pad 31, which isapplied by means of pressurized air supplied to the fluid chamber 8, areadjusted to a desired level. During polishing, the pressure for pressingthe retainer ring 3 against the polishing pad 31 can be varied by meansof the regulator R1, and the pressure for pressing the wafer W againstthe polishing pad 31 can be varied by means of the regulator R2.Consequently, during polishing, by controlling the pressure for pressingthe retainer ring 3 against the polishing pad 31 and the pressure forpressing the wafer W against the polishing pad 31, a uniform pressuredistribution can be obtained continuously across an area from the centerof the wafer W to an outer circumferential portion of the retainer ring3 outside the wafer W. Therefore, excessive or insufficient polishing atthe circumferential edge of the wafer W can be prevented.

In this embodiment, the polishing surface formed on the polishing tablemay be prepared by a polishing pad such as that described above or fixedabrasives. As the polishing pad, various commercially availablepolishing pads, for example, SUBA800, IC-1000 and IC-1000/SUBA400 (atwo-layered cloth) manufactured and sold by Rodel, Inc., and Surfinxxx-5 and Surfin 000 manufactured and sold by FUJIMI INCORPORATED can beused. The SUBA800, Surfin xxx-5 and Surfin 000 are non-woven clothswhich comprise fibers bound by using a urethane resin. The IC-1000comprises a single layer of hard, foamed polyurethane, which has aporous structure and includes a number of fine recesses or holes formedon a surface thereof.

The fixed abrasives comprise particles which are bound by using a binderand formed into a plate. Polishing is conducted by utilizing abrasiveparticles freed from the abrasive plate. The abrasive plate comprisesthe abrasive particles, the binder and pores. Examples of abrasiveparticles include particles of cerium oxide (Ceo2) having an averageparticle diameter of 0.50 m or less. As the binder, for example, anepoxy resin is used. The fixed abrasives provide a hard polishingsurface. The fixed abrasives are generally formed into a disk-like plateand may have a two-layered structure comprising a thin layer of fixedabrasive particles and an elastic polishing pad adhered to a lower sideof the fixed abrasive particles. The above-mentioned IC-1000 alsoprovides a hard polishing surface.

The wafer holder of this embodiment is suitable for use with a polishingmember having a hard polishing surface, and especially suitable for apolishing surface having a modulus of elasticity of compression of 19.6MPa (200 kg/cm2) or more.

In a conventional wafer holder, a wafer is held on a backing padprovided on a rigid wafer holder body. Because the polishing pad iselastic, shocks on the wafer are absorbed mainly by the polishing pad.However, when a hard polishing surface is used, undulation on thepolishing surface is transferred to and affects the wafer surface to bepolished. Further, a mark corresponding to a vacuum opening of thebacking pad is formed on a rear surface of the wafer.

On the other hand, in the wafer holder of this embodiment in which awafer is held on an elastic membrane by utilizing fluid pressure, shockson the wafer due to a hard, undulating polishing surface can be absorbedby the fluid pressure acting on the rear surface of the wafer. Thus,even when the polishing surface is hard, a high polishing performancecan be maintained and no mark corresponding to the vacuum opening isformed on the wafer.

Further, in this embodiment, since the retainer ring is fixedlyconnected to the wafer holder body, the retainer ring can be impartedwith high rigidity and unstable movement of the retainer ring can besuppressed, thereby stabilizing polishing performance.

A highly flattened wafer surface having less scratch marks can beobtained by conducting two-stage polishing, that is, first conductingpolishing of the wafer on a hard abrasive plate while the wafer is heldby the wafer holder of the present invention (i.e., the wafer holderwhich holds a wafer under fluid pressure) and then conducting finalpolishing of the wafer on a polishing pad which is soft as compared tothe abrasive plate while the wafer is held by the wafer holder of thepresent invention. It should be noted that “soft” means having a lowmodulus of elasticity.

FIG. 13 is a plan view of a polishing apparatus which is suitably usedfor the above-mentioned two-stage polishing by using the wafer holder ofthe present invention. The polishing apparatus of FIG. 13 comprises twopolishing tables 30. An abrasive plate or fixed abrasive polishing tool29 is attached to one polishing table 30, to thereby provide a firstpolishing unit 41 a. A polishing pad 31 is attached to the otherpolishing table 30, to thereby provide a second polishing unit 41 b. Thesecond polishing unit 41 b can be used for final polishing. Thepolishing pad 31 of the second polishing unit 41 b has a lower elasticmodulus than that of the polishing tool fixed abrasive polishing tool ofthe first polishing unit 41 a. A wafer holder 1 has the same structureas that shown in FIG. 1 to FIG. 3 or FIG. 9 to FIG. 11. The single waferholder 1 is common to the first polishing unit 41 a and the secondpolishing unit 41 b. That is, as in the case of FIG. 8 or FIG. 12, thewafer holder 1 is supported by a wafer holder head 32. The wafer holderhead is adapted to be pivotally moved by a wafer holder head shaft, andthe wafer holder 1 is capable of moving between the fixed abrasivepolishing tool 29 and the polishing pad 31. In this embodiment, thewafer W is picked up by a wafer holder 1 from a wafer supply lift 42,then moved to the first polishing unit 41 a to conduct a first polishingof the wafer by the fixed abrasive polishing tool 29, thereafter to thesecond polishing unit 41 b to conduct a second or final polishing of thesame by the abrasive pad 31, and returned to the lift 42 to transfer thepolished wafer to the lift. By this arrangement, a highly flattenedwafer surface having fewer scratch marks can be obtained.

It should be noted that the present invention is not necessarily limitedto the foregoing embodiments but can be modified in a variety of wayswithout departing from the gist of the present invention.

1. A substrate holding apparatus for holding a substrate that is to bepolished and bringing it into contact with a polishing surface on apolishing table, the apparatus comprising: a substrate holder body forholding a substrate; a retainer ring integrally formed with or fixedlysecured to the substrate holder body to hold a circumferential edge ofthe substrate; and an elastic membrane and an elastic membranesupporting member contained in an inner space defined by the substrateholder body and the retainer ring, the elastic membrane supportingmember holding an outer circumferential portion of the elastic membrane,wherein the elastic membrane supporting member has a through-holethrough which a pressurized fluid is supplied from a fluid chamber,which is an upper space of the elastic membrane supporting member, to arear surface of the elastic membrane; the elastic membrane has anopening at a central portion thereof, from which opening a suctionportion is exposed, the suction portion being formed on the elasticmembrane supporting member and provided with a communication hole, alower end of which is open; the fluid chamber is supplied with apressurized fluid to press the substrate against the polishing surface;and the communication hole of the suction portion is connected to avacuum source, whereby the substrate is held by the suction portion. 2.A substrate holding apparatus as set forth in claim 1, wherein apressure of the pressurized fluid supplied to the fluid chamber isadjustably changed so as to adjust a polishing pressure against thesubstrate.
 3. A substrate holding apparatus as set forth in claim 2,wherein a vertical position of the elastic membrane supporting memberrelative to the substrate holder body is limited by a restrictionmember.
 4. A substrate holding apparatus as set forth in claim 3,wherein a means for applying a pressing force to the substrate holderbody is a mechanism for moving the substrate holder body in a verticaldirection.
 5. A polishing apparatus comprising a polishing table havinga polishing surface and a substrate holding apparatus as set forth inclaim 3, for holding a substrate that is to be polished and pressing thesubstrate against the polishing surface on the polishing table.
 6. Asubstrate holding apparatus as set forth in claim 2, wherein a means forapplying a pressing force to the substrate holder body is a mechanismfor moving the substrate holder body in a vertical direction.
 7. Apolishing apparatus comprising a polishing table having a polishingsurface and a substrate holding apparatus as set forth in claim 6, forholding a substrate that is to be polished and pressing the substrateagainst the polishing surface on the polishing table.
 8. A polishingapparatus comprising a polishing table having a polishing surface and asubstrate holding apparatus as set forth in claim 2, for holding asubstrate that is to be polished and pressing the substrate against thepolishing surface on the polishing table.
 9. A substrate holdingapparatus as set forth in claim 1, wherein a vertical position of theelastic membrane supporting member relative to the substrate holder bodyis limited by a restriction member.
 10. A substrate holding apparatus asset forth in claim 9, wherein a means for applying a pressing force tothe substrate holder body is a mechanism for moving the substrate holderbody in a vertical direction.
 11. A polishing apparatus comprising apolishing table having a polishing surface and a substrate holdingapparatus as set forth in claim 9, for holding a substrate that is to bepolished and pressing the substrate against the polishing surface on thepolishing table.
 12. A substrate holding apparatus as set forth in claim1, wherein a means for applying a pressing force to the substrate holderbody is a mechanism for moving the substrate holder body in a verticaldirection.
 13. A polishing apparatus comprising a polishing table havinga polishing surface and a substrate holding apparatus as set forth inclaim 12, for holding a substrate that is to be polished and pressingthe substrate against the polishing surface on the polishing table. 14.A polishing apparatus comprising a polishing table having a polishingsurface and a substrate holding apparatus as set forth in claim 1, forholding a substrate that is to be polished and pressing the substrateagainst the polishing surface on the polishing table.
 15. A substrateholding apparatus for holding a substrate that is to be polished andbringing it into contact with a polishing surface on a polishing table,the apparatus comprising: a substrate holder body for holding asubstrate; a retainer ring integrally formed with or fixedly secured tothe substrate holder body to hold a circumferential edge of thesubstrate; and an elastic membrane and an elastic membrane supportingmember contained in an inner space defined by the substrate holder bodyand the retainer ring, the elastic membrane supporting member holding anouter circumferential portion of the elastic membrane, wherein theelastic membrane supporting member has a through-hole through which apressurized fluid is supplied from a fluid chamber, which is an upperspace of the elastic membrane supporting member, to a rear surface ofthe elastic membrane; the elastic membrane has an opening at a centralportion thereof, the opening being provided with a suction portionhaving a communication hole, a lower end of which is open, thecommunication hole being connected to a vacuum source, such that thesuction portion is exposed from the opening, the suction portion beingformed on the elastic membrane supporting member and provided with anelastic sheet that is attached to a lower end surface of the suctionportion; the fluid chamber is supplied with a pressurized fluid to pressthe substrate against the polishing surface, such that a lower endsurface of the elastic sheet is positioned above a lower end surface ofthe elastic membrane while the substrate is being polished; and thecommunication hole of the suction portion is connected to the vacuumsource, whereby the substrate is held by the suction portion, such thatthe lower end surface of the suction portion becomes substantially flushwith the lower end surface of the elastic membrane.
 16. A polishingapparatus comprising a polishing table having a polishing surface and asubstrate holding apparatus as set forth in claim 15, for holding asubstrate that is to be polished and pressing the substrate against thepolishing surface on the polishing table.
 17. A polishing apparatuscomprising a polishing table having a polishing surface and a substrateholder for holding a substrate that is to be polished and bringing itinto contact with the polishing surface on the polishing table, whereinthe substrate holder is provided therein with a fluid chamber defined byan elastic membrane having an opening; a suction portion having acommunication hole is exposed from the opening of the elastic membrane;and an outer circumferential portion of the elastic membrane is held bythe elastic membrane supporting member having a through-hole throughwhich a pressurized fluid is supplied from the fluid chamber to a rearsurface of the elastic membrane, the suction portion being formed on theelastic membrane supporting member, and wherein the fluid chamber issupplied with a pressurized fluid to press the substrate against thepolishing surface, and the communication hole of the suction portion isconnected to a vacuum source, whereby the substrate is held by thesuction portion.
 18. A polishing apparatus as set forth in claim 17,wherein the substrate holder has a retainer ring integrally formed withor fixedly secured to the substrate holder body to hold acircumferential edge of the substrate, such that a pressing force isapplied to the substrate holder body to thereby press the retainer ringagainst the polishing surface.
 19. A polishing apparatus as set forth inclaim 17, wherein the polishing surface is made of a hard abrasivemember having a modulus of compression of 19.6 MPa (200 kg/cm²) or more.20. A polishing apparatus as set forth in claim 17, wherein thepolishing surface comprises fixed abrasive particles fixed in a binderand formed in a plate shape.